1. Field of the Invention
The present invention relates to a plasma addressed electro-optical device of a double layer structure comprising a plasma cell and an electro-optical cell such as a liquid crystal cell, and more particularly to a structure of barrier ribs disposed in a plasma cell serving as a discharge chamber.
2. Description of the Related Art
In a matrix type electro-optical device such as a liquid crystal display device using a liquid crystal cell as an electro-optical cell, there has been generally known heretofore that means for enhancing both the resolution and the contrast is realized by an active matrix addressing system which line-sequentially drives switching elements such as thin film transistors arranged correspondingly to individual picture elements. In this system, however, it is necessary to provide a multiplicity of semiconductor elements like thin film transistors on a substrate, so that if the device is designed to have a great area, there exists a disadvantage that the yield rate in manufacture is rendered lower. Relative to the means for solving such a drawback in the prior art, Buzak et al. proposed a system of utilizing plasma switches in place of switching elements which consist of thin film transistors or the like, as disclosed in U.S. Pat. Nos. 4,896,149 and 5,077,553 corresponding to Japanese Patent Laid-open No. Hei 1 (1989)-217396. Hereinafter a brief explanation will be given on the constitution of a plasma addressed display device which drives a liquid crystal cell by utilizing switches in accordance with plasma discharges. As shown in FIG. 7, this device has a laminated flat panel structure comprising a liquid crystal cell 101, a plasma cell 102 and a common intermediate sheet 103 interposed therebetween. The plasma cell 102 is formed by the use of a glass substrate 104, and a plurality of parallel channels 105 are formed in the surface of the plasma cell 102. The channels 105 extend in the direction of, e.g., rows in a matrix array and are sealed up by the intermediate sheet 103 in a manner to form plasma chambers 106 which are discrete individually. And an ionizable gas is filled in the plasma chambers 106 thus sealed up. A ridge 107 interposed between the mutually adjacent channels 105 serve as a barrier rib to partition the individual plasma chambers 106 while serving also as a gap spacer for the plasma chambers 106. A pair of mutually parallel plasma electrodes 108, 109 are provided in the bottom portion of each channel 105. Each pair of electrodes function as an anode and a cathode to generate discharge plasma by ionizing the gap in the plasma chamber 106. Such discharge region constitutes a row scanning unit.
Meanwhile the liquid crystal cell 101 is composed by the use of a transparent substrate 110. This transparent substrate 110 is disposed opposite to the intermediate sheet 103 through a predetermined gap retained therebetween, and a liquid crystal layer 111 is filled in the gap. On the inner surface of the transparent substrate 110, there are formed signal electrodes 112 composed of a transparent conductive material. The signal electrode 112 is orthogonal to the plasma chambers 106 and constitutes a column driving unit. And picture elements are defined in the form of a matrix at intersections of the column driving units and the row scanning units.
In the display device of the constitution mentioned, the plasma chambers 106 for generation of plasma discharges are line-sequentially switched and scanned, while an analog driving voltage is applied to the signal electrodes 112 on one surface of the liquid crystal cell in synchronism with such scanning to thereby perform driving for display. Upon generation of plasma discharge in the plasma chambers 106, the inside thereof is turned to the anode potential substantially evenly, and picture elements are selected row by row. In other words, the plasma chamber 106 functions as a sampling switch. When the driving voltage is applied to the picture elements during the on-state of the plasma sampling switch, a sample-and-hold operation is performed so that the turn-on or turn-off of each picture element can be controlled. And even after the plasma sampling switch is turned off, the analog driving voltage is still held in the picture element.
In the electro-optical device utilizing discharge plasma as mentioned above, it is considered that a greater effective area is realizable with facility in comparison with any device employing semiconductor elements. However, there still remain a variety of problems unsolved for practical use. For example, the provision of channels 105 for producing plasma chambers 106 on a substrate 104 of a glass material or the like causes considerable difficulties in manufacture, and it is extremely difficult in particular to form the channels 105 at a high density. Furthermore, the etching process for forming discharge plasma electrodes 108 and 109 in the channels 105 is complicated, and there exist some difficulties in attaining a high precision with regard to the space between each pair of electrodes 108 and 109.